Merge pull request #28 from gsalgado/vp

CreateSeries now errors out if given duplicate keys
Add more error codes and messages, refine some doc comments.
Merge pull request #24 from teknico/vp

Add more error codes and message, reflow some doc comments.
Make ReplaceExistingSeriesTest table driven
Merge pull request #29 from larshesel/vp

Make ReplaceExistingSeriesTest table driven